The closest known processes to that of this invention are described in Koslow U.S. Pat. Nos. 5,019,311; 5,147,722; 5,189,092; 5,249,948; and 5,331,037, their parent applications, their corresponding foreign patent applications and patents, and the references cited therein.
The above-mentioned patents disclose processes for the production of composite materials which are characterized by primary particles interconnected by a binder material. Some of these processes require high pressure and shear or extrusion through a die with carefully controlled back pressure. These prior art processes are extremely useful in producing a wide variety of articles including extruded solid forms such as activated carbon filters.
It would often be desirable to impregnate, cover, or otherwise treat a relatively fragile web base material with an active component such as a powdered adsorbent or absorbent material. One example would be a nonwoven medium coated with agents having water absorption and odor adsorption characteristics as in a diaper or hygiene product. A number of other related products will be apparent to those skilled in the art such as, for example, coated paper tissues and toweling, and fabrics such as surgical bandages and sanitary napkins. However, the fragile nature of the underlying base material would make it impractical to employ the known prior art techniques which require high pressure and shear.
In the prior art referred to above, the powdered active material is formed into a self-supporting structure by fusion of a thermoplastic material with which it is intimately mixed. However, the pressures, temperatures, and shear involved, or the process equipment used would not permit their application to fragile substrates such as the webs described herein. Accordingly, it is a primary object of the present invention to provide a method for continuously coating a relatively fragile web with a dry mixture of at least one particulate active material and a very finely divided particulate thermoplastic binder. Other objects, features, and advantages will become apparent from the following description and appended claims.